2.1. Compositions Containing Dihydroxyacetone
Dihydroxyacetone ("DHA") is a white, crystalline, hygroscopic powder having the chemical formula C.sub.3 H.sub.6 O.sub.3. DHA is a three-carbon sugar, normally found as a dimer in freshly prepared aqueous solutions. U.S. Pat. No. 2,949,403 discloses compositions and methods of using DHA as a tanning agent for the human epidermis. When applied topically, DHA penetrates superficially into the stratum corneum where it covalently binds to epidermal proteins via their amino groups, producing a cosmetically-acceptable "tan" color.
U.S. Pat. No. 2,949,403 discloses that DHA may be used in concentrations varying from 0.05 to about 90.0 percent by weight. However, commercial tanning products typically contain only up to about 5% DHA because higher concentrations do not provide an acceptable artificial tan. Occasionally, self-tanning compositions may contain as much as 7.5% DHA. The amount of DHA present in these products depends on a number of factors, including the difficulty in formulating acceptable compositions with higher concentrations of DHA. Likewise, a concentration of about 5% DHA is usually sufficient to provide the coveted artificial "tan" coloring. Many times, higher concentrations of DHA result in skin color much darker or different in color than the desired "tan" color sought to be duplicated.
Particularly, higher concentrations provide color that do not resemble natural tans or darkens the skin to an unacceptable level for the consumer.
Since the 1960's, several compositions using DHA as an active ingredient to impart an artificial tan have been disclosed. For example, U.S. Pat. No. 4,708,865 discloses a topical solution containing DHA and various dyes to offset the undesirable orange cast or hue which results from the use of DHA on fair skinned individuals.
Further, it is well known to formulate DHA into a variety of different carriers such as oil-in-water emulsions, preparations containing up to 50% alcohol, creamy bases and other conventional carrier systems such as lotions, ointments, dusting powders and the like. These compositions typically include a number of other optional ingredients such as perfumes, preservatives, emollients, antiseptics, pigments, dyes, humectants, as well as other materials that may be cosmetically or medicinally desirable. In particular, many commercial products contain materials which act as penetration enhancers in that they promote the absorption of the DHA deep into the skin tissue layers in order to increase the length of time the artificial tan remains.
In addition to its ability to elicit an artificial tan on human skin, it is also known that the reaction product of DHA and compounds in the skin tissue which produces the "tan" color is an effective sunscreening agent. In particular, this reaction product is known to absorb ultraviolet light in the 300-600 nanometer range, with a peak at about 350 nanometers, thus protecting the skin from damage due to exposure to such radiation.